Distractor for use in spinal surgery

ABSTRACT

Apparatus and a method of inserting spinal implants is disclosed in which an intervertebral space is first distracted, a hollow sleeve having teeth at one end is then driven into the vertebrae adjacent that disc space. A drill is then passed through the hollow sleeve removing disc and bone in preparation for receiving the spinal implant which is then inserted through the sleeve.

[0001] This application is a continuation of application Ser. No.09/626,636, filed Jul. 27, 2000; which is a continuation of applicationSer. No. 08/484,927, filed Jun. 7, 1995, now U.S. Pat. No. 6,096,038;which is a divisional of 08/074,781, filed Jun. 10, 1993, now U.S. Pat.No. 5,484,437; all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to artificial fusion implants to beplaced into the intervertebral space left remaining after the removal ofa damaged spinal disc and specifically to the apparatus for and methodof, inserting the implants.

[0004] 2. Description of the Prior Art

[0005] For the purpose of achieving long term stability to a segment ofinjured spine, a fusion (the joining together of two or more bones via acontinuous bridge of incorporated bone) may be performed. Well-known tothose skilled in such art is the interbody fusion wherein the disc ispartially excised and bone placed within that space previously occupiedby that disc material (between adjacent vertebrae) for the purpose ofrestoring a more normal spatial relationship, and to provide forstability; short term by mechanical support, and long term by thepermanent cross bonding of bone from vertebra to vertebra. For fusion tooccur within the disc space, it is necessary to prepare the vertebrae tobe fused by breaking through, or cutting into, the hardened outsideplates of bone (the endplates) to allow the interposed bone graft tocome into direct contact with the more vascular cancellous (spongy)bone, and to thereby trick the body into attempting to heal thisinduced, but controlled, “fracturing” by both bone production and thehealing of the grafts to both opposed vertebral surfaces such that theybecome one continuous segment of bone.

[0006] The purpose of the present invention is to provide an implant,and the apparatus and method of inserting the implant within theintervertebral space left after the removal of the disc material andpermanently eliminate all motion at that location. To do so, the deviceof the present invention is space occupying within the disc interspace,rigid, self-stabilizing to resist dislodgement, stabilizing to theadjacent spinal vertebrae to eliminate local motion, and able tointrinsically participate in a vertebra to vertebra bony fusion so as toassure the permanency of the result.

[0007] At present, following the removal of a damaged disc, either boneor nothing is placed into the remaining space. Placing nothing into thisspace allows the space to collapse which may result in damage to thenerves; or the space may fill with scar tissue and eventually lead to areherniation. The use of bone to fill the space is less than optimal inthat bone obtained from the patient requires additional surgery and isof limited availability in its most useful form, and if obtainedelsewhere, lacks living bone cells, carries a significant risk ofinfection, and is also limited in supply as it is usually obtained fromaccident victims. Furthermore, regardless of the source of the bone, itis only marginal structurally and lacks a means to either stabilizeitself against dislodgement, or to stabilize the adjacent vertebrae.

[0008] a. Prior Art Implants

[0009] There have been an extensive number of attempts to develop anacceptable disc prosthesis (an artificial disc). Such devices by designwould be used to replace a damaged disc and seek to restore the heightof the interspace and to restore the normal motion of that spinal joint.No such device has been found that is medically acceptable. This groupof prosthetic or artificial disc replacements, seeking to preservespinal motion and so are different from the present invention, wouldinclude:

[0010] U.S. Pat. No. 3,867,728 to STUBSTAD—describing a flexible discimplant.

[0011] U.S. Pat. No. 4,349,921 to KUNTZ—describing a flexible discreplacement with file-like surface projections to discourage devicedislocation.

[0012] U.S. Pat. No. 4,309,777 to PATIL—describing a motion preservingimplant with spiked outer surfaces to resist dislocation and containinga series of springs to urge the vertebrae away from each other.

[0013] U.S. Pat. No. 3,875,595 to FRONING—describing a motion preservingbladder-like disc replacement with two opposed stud-like projections toresist dislocation.

[0014] U.S. Pat. No. 2,372,622 to FASSIO (France)—describing a motionpreserving implant comprising complimentary opposed convex and concavesurfaces.

[0015] In summary, these devices resemble the present invention only inthat they are placed within the intervertebral space following theremoval of a damaged disc. In that they seek to is preserve spinalmotion, they are diametrically different from the present inventionwhich seeks to permanently eliminate all motion at that spinal segment.

[0016] A second related area of prior art includes those devicesutilized to replace essentially wholly removed vertebrae. Such removalis generally necessitated by extensive vertebral fractures, or tumors,and is not associated with the treatment of disc disease. While thepresent invention is to be placed within the disc space, these othervertebral devices cannot be placed within the disc space as at least onevertebra has already been removed such that there no longer remains a“disc space”. Furthermore, these devices are limited in that they seekto perform as temporary structural members mechanically replacing theremoved vertebrae (not a removed disc), and do not intrinsicallyparticipate in supplying osteogenic material to achieve cross vertebraebony fusion. Therefore, unlike the present invention which provides fora source of osteogenesis, use of this group of devices must beaccompanied by a further surgery consisting of a bone fusion procedureutilizing conventional technique. This group consisting of vertebralstruts rather than disc replacements would include the following:

[0017] U.S. Pat. No. 4,553,273 to WU—describing a turnbuckle-likevertebral strut.

[0018] U.S. Pat. No. 4,401,112 to REZAIAN—describing a turnbuckle-likevertebral strut with the addition of a long stabilizing staple thatspans the missing vertebral body.

[0019] U.S. Pat. No. 4,554,914 to KAPP—describing a large distractiblespike that elongates with a screw mechanism to span the gap left by theremoval of an entire vertebra and to serve as an anchor for acryliccement which is then used to replace the missing bone (vertebrae).

[0020] U.S. Pat. No. 4,636,217 to OGILVIE—describing a vertebral strutmechanism that can be implanted after at least one vertebrae has beenremoved and consists of a mechanism for causing the engagement of screwsinto the vertebrae above and the vertebrae below the one removed.

[0021] In summary, this second group of devices differs from the presentinvention in that they are vertebral replacements struts, do notintrinsically participate in the bony fusion, can only be inserted inthe limited circumstances where an entire vertebra has been removed fromthe anterior approach, and are not designed for, or intended to be usedfor the treatment of disc disease.

[0022] A third area of prior art related to the present inventionincludes all devices designed to be applied to one of the surfaces ofthe spine. Such devices include all types of plates, struts, and rodswhich are attached by hooks, wires and screws. These devices differsignificantly from the present invention in that they are not insertedwithin the disc space and furthermore do not intrinsically participatein supplying osteogenic material for the fusion.

[0023] Therefore, where permanent spinal immobilization is desired, anadditional surgery, consisting of a spinal fusion performed byconventional means or the use of supplemental methylmethacrylate cementis required. Such devices applied to the spine, but not within the discspace, would include the following:

[0024] U.S. Pat. No. 4,604,995 to STEPHENS—describing a “U” shaped metalrod attached to the posterior elements of the spine with wires tostabilize the spine over a large number of segments.

[0025] U.S. Pat. No. 2,677,369 to KNOWLES—describing a metal columndevice to be placed posteriorly along the lumbar spine to be held inposition by its shape alone and to block pressure across the posteriorportions of the spinal column by locking the spine in full flexionthereby shifting the maximum weight back onto the patient's own disc.

[0026] Other devices are simply variations on the use of rods (e.g.Harrington, Luque, Cotrel-Dubosset, Zielke), wires or cables (Dwyer),plates and screws (Steffee), or struts (Dunn, Knowles).

[0027] In summary, none of these devices are designed to be nor can beused within the disc space. Moreover, these devices do not replace adamaged disc, and do not intrinsically participate in the generation ofa bony fusion.

[0028] Another area of related prior art to be considered is that ofdevices designed to be placed within the vertebral interspace followingthe removal of a damaged disc, and seeking to eliminate further motionat that location.

[0029] Such a device is contained in U.S. Pat. No. 4,501,269 issued toBAGBY which describes an implantable device and limited instrumentation.The method employed is as follows: a hole is bored transversely acrossthe joint and a hollow metal basket of larger diameter than the hole isthen pounded into the hole and then the hollow metal basket is filledwith the bone debris generated by the drilling.

[0030] While the present invention (device, instrumentation, and method)may appear to bear some superficial resemblance to the BAGBY invention,it is minimal, while the differences are many fold and highlysignificant. These differences include the following:

[0031] 1. Safety—The present invention provides for a system ofcompletely guarded instrumentation so that all contiguous vitalstructures (e.g. large blood vessels, neural structures) are absolutelyprotected. The instrumentation of the present invention also makesoverpenetration by the drill impossible. Such overpenetration in thecervical spine, for example, would result in the total paralysis ordeath of the patient. In the thoracic spine, the result would becomplete paraplegia. In the lumbar spine, the result would be paraplegiaor a life-threatening perforation of the aorta, vena cava, or iliacvessels.

[0032] The present invention is atraumatically screwed into place whilethe BAGBY device, in contradistinction, is pounded into position. BAGBYdescribes that its implant is significantly larger in size than the holedrilled and must be pounded in. This is extremely dangerous and thepounding occurs directly over the spinal cord which is precariouslyvulnerable to percussive injury. Furthermore, while it is possible, forexample in the lumbar spine, to insert the present invention away fromthe spinal cord and nerves, the BAGBY device must always be poundeddirectly towards the spinal cord.

[0033] Furthermore, since the BAGBY device is pounded into a smooth holeunder great resistance, and lacking any specific design features tosecure it, the device is highly susceptible to forceful ejection whichwould result in great danger to the patient and clinical failure. Thepresent invention, in contradistinction, is securely screwed into place,and possesses highly specialized locking threads to make accidentaldislodgement impossible. Because of the proximity of the spinal cord,spinal nerves, and blood vessels, any implant dislodgement as mightoccur with the BAGBY device might have catastrophic consequences.

[0034] 2. Broad applicability—The BAGBY device can only be inserted fromthe front of the vertebral column, however, in contrast, the presentinvention can be utilized in the cervical, thoracic, and lumbar spine,and can be inserted from behind (posteriorly) in the lumbar spine. Thisis of great importance in that the purpose of these devices is in thetreatment of disc disease and probably greater than 99 percent of alllumbar operations for the treatment of disc disease are performed frombehind where the present invention can easily be utilized, but the BAGBYdevice, as per BAGBY'S description, cannot.

[0035] 3. Disc removal—The BAGBY invention requires the complete removalof the disc prior to the drilling step, whereas the present inventioneliminates the laborious separate process of disc removal andefficiently removes the disc and prepares the vertebral end plates in asingle step.

[0036] 4. Time required—The present invention saves time over the BAGBYinvention since time is not wasted laboring to remove the disc prior toinitiating the fusion. Also, with the present invention the procedure isperformed through a system of guarded instrumentation, time is notwasted constantly placing and replacing various soft tissue retractorsthroughout the procedure.

[0037] 5. Implant stability—Dislodgement of the implant would be a majorsource of device failure (an unsuccessful clinical result), and mightresult in patient paralysis or even death. As discussed, the BAGBYdevice lacks any specific means of achieving stability and since it ispounded in against resistance to achieve vertebral distraction, and issusceptible to forceful dislodgement by the tendency of the twodistracted vertebrae, to return to their original positions squeezingout the device. The present invention, however, is screwed into place.As there is no unscrewing force present between the vertebrae,compression alone cannot dislodge the implant. The implant is inherentlystable by its design. Furthermore, the threads of the present inventionare highly specialized in that they are periodically interrupted so thatthe tail ends of each of the tabs so formed are blunted and twisted soas to resist accidental unscrewing. The removal of an implant with such“locking threads” requires the use of a special extractor includedwithin the instrumentation. The stability of the present invention isstill further enhanced, again in contradistinction to the BAGBY device,by the presence of a “bone ingrowth” surface texturing, which bothincreases the friction of the fit and allows for the direct growth ofthe vertebral bone into the casing of the implant itself.

[0038] 6. Spinal stability—The present invention is not onlyself-stabilizing, it also provides stability to the adjacent vertebraein at least three ways that the BAGBY device cannot. First, the BAGBYdevice is placed transversely across the joint in the center, leavingboth vertebrae free to rock back and forth over this round barrel shapedaxis, much like a board over a barrel, being used for a seesaw.

[0039] Secondly, as the BAGBY device lacks any specific design featuresto resist sliding, it may actually behave as a third body allowing thetranslation of the vertebrae relative to the device and to each other.

[0040] Thirdly, any device can only provide stability if it remainsproperly, seated. The present invention is inherently stable, andtherefore assures that it will stabilize the adjacent vertebrae, ratherthan, as with the BAGBY, the instability of the spine to be treated maycause a dislocation of the BAGBY implant, is with further loss of spinalstability.

[0041] 7. The collapse of the interspace—While both the presentinvention and the BAGBY device can be fabricated to withstand thecompression forces within the interspace, the interspace maynevertheless collapse under the superincumbent body weight as theimplant settles into the vertebral bone. This is related to the load perunit area. Again the present invention is superior to the BAGBY devicein at least four ways.

[0042] First, the present invention offers considerably greater surfacearea to distribute the load. Secondly, while the BAGBY device is placedcentrally, the present device is placed bilaterally where the bone tendsto be more cortical and much stronger out towards the rim. Thirdly, thepresent invention supports the load achieving an “I” beam effect,whereas the BAGBY implant does not. Fourthly, it is not pressure alonethat causes the collapse of the bone adjacent to the implant, but alsobony erosion that is caused by the motion under pressure of the implantagainst the bone. As discussed in item 6 above, the present inventionalone is highly resistant to such motion, again diminishing thelikelihood of erosion and interspace collapse.

[0043] 8. Bone ingrowth surface texturing—The present invention has asurface treatment of known and conventional technology to induce thegrowth of bone from the vertebrae directly into the casing material ofthe implant itself. The BAGBY device has no similar feature.

[0044] 9. Fusion mass—The BAGBY invention calls for removing the discand then drilling a hole between the adjacent vertebrae. The bony debrisso generated is then put into the device. The present invention takes acore of pure bone producing marrow from the iliac crest, and then by useof a special press, forcibly injects the implant device with anextremely dense compressed core of that osteogenic material until thematerial itself virtually extrudes from every cell of the implant.

[0045] 10. The probability of achieving fusion—The fusion rate withinthe spine is known to be related directly to the amount of exposedvascular bone bed area, the quality and quantity of the fusion massavailable, and the extent of the stabilization obtained with all otherfactors being half constant. It would then be anticipated, that thefusion rate would be superior with the present invention as compared tothe RAGBY device, because of optimal implant stability (#5), optimalspinal stability (#6), bone ingrowth surface treatment (#8), superiorfusion mass (#9), and the greater exposed vertebral bony surface area(#7).

[0046] The last area of prior art possibly related to the presentinvention and therefore, to be considered related to “bony ingrowth”,are patents that either describe methods of producing materials and ormaterials or devices to achieve the same. Such patents would include:

[0047] U.S. Pat. No. 4,636,526 (DORMAN), No. 4,634,720 (DORMAN), No.4,542,539 (ROWE), No. 4,405,319 (COSENTINO), No. 4,439,152 (SMALL), No.4,168,326 (BROEMER), No. 4,535,485 (ASHMAN), No. 3,987,499 (SCHARBACH),No. 3,605,123 (HAHN), No. 4,655,777 (DUNN), No. 4,645,503 (LIN), No.4,547,390 (ASHMAN), No. 4,608,052 (VAN KAPEN), No. 4,698,375 (DORMAN),No. 4,661,536 (DORMAN), No. 3,952,334 (BOKROS), No. 3,905,047 (LONG),No. 4,693,721 (DUCHEYNE), No. 4,070,514 (ENTHERLY).

[0048] However, while the implant of the present invention would utilizebone ingrowth technology, it would do so with conventional technology.

[0049] b. Prior Art Instrumentations and Methods

[0050] The following is a history of the prior art apparatus and methodsof inserting spinal implants:

[0051] In 1956, Ralph Cloward developed a method and instruments whichhe later described for preparing the anterior aspect (front) of thecervical spine, and then fusing it. Cloward surgically removed the discto be fused across and then placed a rigid drill guide with a large footplate and prongs down over an aligner rod and embedded said prongs intothe adjacent vertebrae to maintain the alignment so as to facilitate thereaming out of the bone adjacent the disc spaces. As the large footplate sat against the front of the spine, it also served as a fixedreference point to control the depth of drilling. The reaming left twoopposed resected arcs, one each, from the opposed vertebral surfaces.The tubular drill guide, which was placed only preliminary to thedrilling, was thereafter completely removed. A cylindrical bony dowel,significantly larger in diameter than the hole formed, was then poundedinto the hole already drilled. Cloward's method of instrumentation wasdesigned for, and limited to, use on the anterior aspect and in theregion of the cervical spine only. The hole was midline, which wouldpreclude its use posteriorly where the spinal cord would be in the way.

[0052] As the bone graft to be inserted in Cloward's method wasnecessarily larger in diameter than the hole drilled, the graft couldnot be inserted through the drill guide. This mandated the removal ofthe drill guide and left the graft insertion phase completelyunprotected. Thus Cloward's method and instrumentation was inappropriatefor posterior application.

[0053] In addition, the failure to provide continuous protection to thedelicate neural structures from the instruments, as well as the bony andcartilaginous debris generated during the procedure, made Cloward'smethod inappropriate for posterior application. Also, the drill guidedescribed by Cloward could not be placed posteriorly within the spinalcanal, as the foot plate would crush the nerves. Modifying Cloward'sdrill guide by removing the foot plate completely, would still leave theinstrument unworkable as it would then lack stability, and would not becontrollable for depth of seating.

[0054] Nevertheless, Wilterberger, (Wilterberger, B. R., Abbott, K. H.,“Dowel Intervertebral Fusion as Used in Lumbar Disc Surgery,” TheJournal of Bone and Joint Surgery, Volume 39A, pg. 234-292, 1957)described the unprotected drilling of a hole from the posterior into thelumbar spine between the nerve roots and across the disc space, and theninserting a stack of button-like dowels into that space. WhileWilterberger had taken the Cloward concept of circular drilling anddowel fusion and applied it to the lumbar spine from a posteriorapproach, he had not provided for an improved method, nor had headvanced the instrumentation so as to make that procedure sufficientlysafe, and it rapidly fell into disrepute.

[0055] Crock (Crock, H. V., “Anterior Lumbar InterbodyFusion—Indications for its Use and notes on Surgical Technique,”Clinical Orthopedics, Volume 165, pg. 157-163, 1981) described histechnique and instrumentation for Anterior Interbody Fusion of thelumbar spine, wherein he drilled two large holes side by side across thedisc space from anterior to posterior essentially unprotected and thenpounded in two at least partially cylindrical grafts larger than theholes prepared.

[0056] A review of the prior art is instructive as to a number ofsignificant deficiencies in regard to the method and instrumentation forthe performance of Interbody Spinal Fusion utilizing drilling to preparethe endplates.

[0057] As the great majority of spinal surgery is performed in thelumbar spine and from posteriorly, a review of the prior art reveals anumber of deficiencies in regard to the spine in general, and to theposterior approach to the lumbar spine specifically. These deficienciesinclude the:

[0058] 1. Failure to protect the surrounding tissues throughout theprocedure, specifically, prior to drilling and until after the insertionof the graft;

[0059] 2. Failure to contain the debris, bony and cartilaginous,generated during the procedure;

[0060] 3. Failure to optimize the contact of the cylindrical drill holeand bone graft, the mismatch in their diameters resulting inincongruence of fit;

[0061] 4. Failure to determine the optimal drill size prior to drilling;

[0062] 5. Failure to determine the optimal amount of distraction priorto drilling;

[0063] 6. Inability to optimize the amount of distraction so as torestore the normal spatial relationships between adjacent vertebrae;

[0064] 7. Inability to create sufficient working space within the spinalcanal (between the nerve roots and the dural sac) to make the proceduresafe;

[0065] 8. Absent a foot plate on the drill guide, as necessitated by theclose tolerances posteriorly, the inability to reliably insure that thedrilling is parallel to the vertebral endplates;

[0066] 9. The inability to insure equal bone removal from the opposedvertebral surfaces; and

[0067] 10. The inability to determine within the spinal canal, theproper side by side positioning for dual drill holes.

SUMMARY OF THE INVENTION

[0068] The present invention comprises a series of artificial implants,the purpose of which is to participate in, and directly cause bonefusion across an intervertebral space following the excision of adamaged disc. Such implants are structurally load bearing devices,stronger than bone, capable of withstanding the substantial forcesgenerated within the spinal interspace. The devices of the presentinvention have a plurality of macro sized cells and openings, which canbe loaded with fusion promoting materials, such as autogenous bone, forthe purpose of materially influencing the adjacent vertebrae to performa bony bond to the implants and to each other. The implant casing may besurface textured or otherwise treated by any of a number of knowntechnologies to achieve a “bone ingrowth surface” to further enhance thestability of the implant and to expedite the fusion.

[0069] The devices of the present invention are configured and designedso as to promote their own stability within the vertebral interspace andto resist being dislodged, and furthermore, to stabilize the adjacentspinal segments.

[0070] The apparatus and method of the present invention for preparingthe vertebrae for insertion of the implant allows for the rapid and saferemoval of the disc, preparation of the vertebrae, performance of thefusion, and internal stabilization of the spinal segment.

[0071] The present invention is a method for Interbody Spinal Fusionutilizing novel instrumentation, whereby a protective tubular member isplaced prior to the drilling part of the procedure and is left in placeuntil the graft is fully seated.

[0072] In the preferred embodiment two distractors are used to separatetwo adjacent vertebrae to a preferred distance. A hollow Outer Sleevehaving teeth at one end is driven into the adjacent vertebrae on oneside to hold the vertebrae in position when the distractor is removed, adiameter reducing hollow Inner Sleeve is introduced into the OuterSleeve, a drill having a drill stop is passed through the hollow InnerSleeve to drill a hole to a desired depth, and an implant is inserted inthe hole. The method is repeated on the other side of the disc.

[0073] In summary then, the present invention, instrumentation, andmethod, provides for a single surgery providing for an integrateddiscectomy, fusion, and interbody internal spinal fixation.

[0074] Discussion of the Instrumentation

[0075] The apparatus and method of the present invention provide thefollowing advantages:

[0076] 1. The present invention is safer by providing protection of thesurrounding tissues. An Outer Sleeve places all of the delicate softtissue structures, nerves, blood vessels, and organs outside of the pathof the various sharp surgical instruments and the implant. Further, itis an improvement upon hand held retractors in that it occupies theleast possible amount of area, avoids the stretching associated withmanual retraction, provides for the retraction and shielding of thesurrounding tissues in all directions circumferentially andsimultaneously, and it does so exclusively with smooth, curved surfaces.

[0077] 2. The present invention is safer by providing protection againstthe danger of instrument or implant overpenetration.

[0078] 3. The present invention is safer as the surgical site and woundare protected from the debris generated during the procedure.

[0079] 4. The present invention is safer because the method provides forabsolute protection to the soft tissues directly and from indirectinjury by overpenetration. It makes safe the use of powerinstrumentation which is both more effective and efficient.

[0080] 5. The present invention maintains the vertebrae to be fusedrigid throughout the procedure.

[0081] 6. The present invention holds the vertebrae to be fused alignedthroughout the procedure.

[0082] 7. The present invention holds the vertebrae to be fuseddistracted throughout the procedure.

[0083] 8. The present invention assures that all instruments introducedthrough the Outer Sleeve are coaxial and equally centered through thedisc space and parallel the endplates.

[0084] 9. The present invention facilitates the implant insertion bycountering the high compressive forces tending to collapse theinterspace, which if left unchecked would resist the introduction andadvancement of the implant and make stripping more likely.

[0085] 10. The present invention extends the range and use of theprocedure and similarly the interbody spinal implant itself by makingthe procedure safe throughout the spine.

[0086] 11. The present invention increases the ability to use aspecifically sized implant.

[0087] 12. In the present invention the end of all the penetratinginstrumentation is blunt faced.

[0088] 13. In the present invention all of the instruments have beenstopped at a predetermined depth to avoid overpenetration.

[0089] 14. The design of the Outer Sleeve in the present inventionconforms to the spacial limitations of the specific surgical site.

[0090] 15. The design and use of a second or Inner Sleeve in the presentinvention allows for the difference in size between the inside diameterof the Outer Sleeve, and the outside diameter of the drill itself. Thisdifference being necessary to accommodate the sum of the distraction tobe produced, and the depth of the circumferential threading present ofthe implant.

[0091] 16. In the present invention a specially designed drill bit witha central shaft recess allows for the safe collection of the drillingproducts, which can then be removed without disturbing the Outer Sleeveby removing the drill bit and Inner Sleeve as a single unit.

[0092] 17. In the present invention a specially designed trephine forremoving a core of bone slightly smaller in diameter than the internaldiameter of the implant cavity itself, however of a greater length.

[0093] 18. In the present invention a specially designed press forforcefully compressing and injecting the long core of autogenous boneinto the implant, such that it extrudes through the implant itself.

[0094] 19. In the present invention a specially designed driverextractor, which attaches to the implant and allows the implant to beeither inserted or removed without itself dissociating from the implant,except by the deliberate disengagement of the operator.

[0095] 20. In the present invention predistraction increases the workingspace.

[0096] 21. The Distractor in the present invention is self-orientingacting as a directional finder.

[0097] 22. The Distractor in the present invention is self-centralizingbetween the opposed vertebral surfaces acting as a centering post forthe subsequent bone removal.

[0098] 23. In the present invention predistraction assures the equalremoval of bone from the adjacent vertebral surfaces.

[0099] 24. In the present invention predistraction assures the exactcongruence between the hole drilled and the device.

[0100] 25. In the present invention predistraction assures that thedrilling is parallel to the vertebral endplates.

[0101] 26. In the present invention predistraction allows for thedetermination of the optimal distraction prior to drilling.

[0102] 27. In the present invention predistraction allows for theverification of the correct prosthesis size prior to drilling.

[0103] 28. In the present invention predistraction facilitates deviceinsertion by relieving the compressive loads across the interspace whichwould resist implantation.

[0104] 29. In the present invention predistraction decreases thelikelihood of stripping the bone during insertion.

[0105] 30. In the present invention predistraction provides for the sideby side positioning, spacing, and parallelism required prior to theirrevocable event of drilling.

[0106] 31. In the present invention predistraction provides for therigid stabilization of the vertebrae opposed to the disc spacethroughout the surgical procedure.

[0107] 32. In the present invention predistraction provides for animplant easier to insert as the compressive loads of the opposedvertebrae are held in check so that the device itself need not drive thevertebrae apart to be inserted.

[0108] 33. In the present invention predistraction allows for theinsertion of a more effective implant as more of the implant can bededicated to its intended purpose and be full diameter, whereas withoutthe benefit of predistraction and the ability to maintain the same, asignificant portion of the forward end of the implant would need to bededicated to the purpose of separating the opposing vertebrae.

[0109] 34. The present invention allows for the use of an implant with asharper thread or surface projections as there is no danger to thesurrounding tissues.

[0110] 35. The present invention allows for the implant to be fullypreloaded as provided to the surgeon, or for the surgeon to load it withthe material of his choice at the time of surgery.

[0111] 36. The present invention allows for the loading of a spinalimplant outside of the spinal canal and prior to implantation.

OBJECTS OF THE PRESENT INVENTION

[0112] It is an object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, and specifically, all three of the abovesimultaneously and as a single procedure.

[0113] It is another object of the present invention to provide animproved method of performing a discectomy, a fusion, and an internalstabilization of the spine, which is both quicker and safer than ispossible by previous methods.

[0114] It is another object of the present invention to provide animproved method of performing a discectomy, a fusion and an internalstabilization of the spine, to provide for improved surgical spinalimplants.

[0115] It is another object of the present invention to provide animproved method of performing a discectomy, a fusion, and an internalstabilization of the spine, which provides for an improved system ofsurgical instrumentation to facilitate the performance of the combineddiscectomy, fusion, and internal spinal stabilization.

[0116] It is another object of the present invention to provide animproved method of performing a discectomy, a fusion, and an internalstabilization of the spine procedures.

[0117] It is an object of the present invention to provideinstrumentation and a method of spinal interbody arthrodesis that isfaster, safer, and more efficacious than prior methods, and caneffectively be performed in the cervical, thoracic, and lumbar spineanteriorly, as well as in the lower lumbar spine posteriorly.

[0118] It is a further object of the present invention to provide ameans for inserting a spinal implant between adjacent vertebrae whilemaintaining their optimal spacing, positioning, and alignment.

[0119] These and other objects of the present invention will be apparentfrom review of the following specification and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0120]FIG. 1 is a side view of the Long Distractor, of the presentinvention inserted into the intervertebral space.

[0121]FIG. 2 is a side view of a Convertible Distractor assembly inrelation to the spine.

[0122]FIG. 3 is a perspective view of a high retention Short Distractorof FIG. 2.

[0123]FIG. 3A is a side view of the high retention Short Distractor ofFIG. 2.

[0124]FIG. 3B is a side view of an alternative Short Distractor withcircumferential forward facing ratcheting.

[0125]FIG. 3C is a top view of the alternative Short Distractor of FIG.3B.

[0126]FIG. 3D is a perspective view of an alternative embodiment of aShort Distractor.

[0127]FIG. 3E is a top view of the alternative distractor of FIG. 3D.

[0128]FIG. 3F is a side view of a further alternative rectangularizedShort Distractor with knurled surfaces.

[0129]FIG. 4 is a perspective view of a spinal segment (two vertebraeand an interposed disc) with a Short Distractor in place, with a portionof the upper vertebrae and disc cut away to show the Short Distractor onone side of the spine and the Long Distractor about to be placedcontralaterally.

[0130]FIG. 5 shows a side view of the Outer Sleeve in place over theLong Distractor, and about to receive the Driver Cap in preparation forbeing seated.

[0131]FIG. 6 shows the Long Distractor, Outer Sleeve, and Driver Capfollowing the proper seating of the Outer Sleeve into the two adjacentvertebrae.

[0132]FIG. 7A is a side view of the cervical Outer Sleeve being placedover a Long Distractor which is in place within the disc spaceanteriorly.

[0133]FIG. 7B is a bottom view of the single Outer Sleeve of FIG. 7A.

[0134]FIG. 7C is a bottom view of a Dual Outer Sleeve.

[0135]FIG. 7D is an enlarged side view of the proximal portion of FIG.7C.

[0136]FIG. 7E is a bottom view of a Dual Driver Cap for driving twodistractors.

[0137]FIG. 7F is a side sectional view showing the Dual Outer Sleeve ofFIGS. 7C and 7D, Distractors and Dual Cap of FIG. 7E seated.

[0138]FIG. 8 is a side view of the Outer Sleeve of FIG. 7A centered onthe Long Distractor and fully seated on the anterior aspect of thecervical spine.

[0139]FIG. 9 is a perspective view of the Distractor Puller.

[0140]FIG. 10 is a cutaway partial side view of the Proximal Pullerengaging the extraction ring of the Long Distractor over the end of theOuter Sleeve.

[0141]FIG. 10A is a side view of the Puller coupled to the LongDistractor just prior to its extraction.

[0142]FIG. 10B is a posterior view of the proximal Outer Sleeve and aShort Distractor in place in regard to the vertebrae, disc and nerves.

[0143]FIG. 11A is a side sectional view of the Drill and Inner Sleevewithin the Outer Sleeve and drilling across the intervertebral space andcutting partially cylindrical arcs from the adjacent vertebrae.

[0144]FIG. 11B is a sectional side view of preparation of theintervertebral space by the alternative “Trephine Method” showing theDistractor, Trephine, Inner Sleeve, and Outer Sleeve in place.

[0145]FIG. 11C is a sectional side view as in FIG. 11A, but showing theuse of an alternative drilling conformation wherein the extendedproximal portion is both distracting and self-centering.

[0146]FIG. 11D is a side view of an instrument for removing arcs of bonefrom vertebrae following drilling.

[0147]FIG. 12 is a perspective view of the surgical Tap.

[0148]FIG. 13 is a side view of the Outer Sleeve and the surgical Tapfully threaded within the interspace.

[0149]FIG. 14A is a side view of the bone harvesting Trephine and motoradapter.

[0150]FIG. 14B is a perspective view of the implant Bone Loading Device.

[0151]FIG. 14C is a perspective view of the Corkscrew bone freeing andextracting instrument.

[0152]FIG. 15 is a partial perspective view of the Bone Loading Devicein operation.

[0153]FIG. 16 is a perspective view of the Implant Driver about toengage the spinal implant.

[0154]FIG. 17 is a side view of the spinal implant being fully seatedwithin the intervertebral space by means of the Driver apparatus inplace within the Outer Sleeve.

[0155]FIG. 18 is a side view of the lumbar spine showing the end resultof the device implantation via the posterior route.

DETAILED DESCRIPTION OF THE DRAWINGS

[0156] The following discussion will be in regard to application in thelumbar spine via the posterior approach. In its simplest form, themethod of the present invention involves the following steps. Thepatient is placed on a spinal surgery frame, which allows for thedistraction and alignment of the disc space to be fused. A bilateralposterior exposure of the interspace, with or without partial discectomyis then performed. Utilizing distractors the disc space is distracted,and a hollow Outer Sleeve is fitted over one of the distractors. The endof the Outer Sleeve has teeth for engaging the two adjacent vertebrae.The Outer Sleeve is driven into the vertebrae and the distractor is thenremoved. A hollow Inner Sleeve is then inserted into the Outer Sleeveand a stopped Drill is utilized to prepare the opposed vertebralsurfaces. The Drill and the Inner Sleeve are removed as a single unit.The space is tapped if so required. The prepared spinal implant is theninserted via the Outer Sleeve utilizing a stopped inserter. Theinstruments are then removed and the procedure repeated on thecontralateral side of the spine.

[0157] Step 1a. Prior to surgery, translucent implant templatesappropriately adjusted for scale are superimposed on AP, lateral, andaxial images of the interspace to be fused, for the purpose of selectingthe optimal implant size and to determine the desired distraction.

[0158] Step 1b. The patient is preferably placed onto a spinal surgeryframe capable of inducing both distraction and vertebral alignment.

[0159] Step 2. In the preferred embodiment, a standard bilateral(partial) discectomy is performed and any posterior lipping of thevertebral bodies adjacent the interspace is removed. Alternatively, nodisc material need be removed. In the preferred embodiment, theinterspace is exposed by performing bilateral pairedsemihemilaminotomies and resecting the inner aspects of the facet jointsadjacent the spinal canal while preserving the supra and interspinousligaments.

[0160] Step 3. Beginning on the first side, the dural sac and traversingnerve root at that level are retracted medially and a Long Distractorthen inserted and impacted flush to the posterior vertebral bodiesadjacent that interspace. Long Distractors with working ends ofincreasing diameter are then sequentially inserted until the optimaldistraction is obtained. This optimal distraction not only restores thenormal height of the interspace, but further achieves a balance whereinthe tendency for the space to collapse is resisted, which in urging thevertebral bodies apart is being equally resisted by the powerful softtissue structures about the spinal segment including the outer casing ofthe disc (the annulus fibrosus), various ligaments, capsular structures,as well as the muscles and other soft-tissue structures. This balanceddistraction not only provides for the spatial restoration of the heightof the interspace, but for considerable stability as the space nowresists further distraction or collapse.

[0161] In the preferred embodiment, as the desired distraction isapproached, the use of the solid bodied Long Distractors is terminatedand a disassemblable Convertible Distractor is placed with tactileand/or radiographic confirmation of ideal distraction. The ConvertibleDistractor is then disassembled such that the Short Distractor portionis left in place and the ultra-low profile head portion being positionedadjacent to the canal floor and safely away from the neural structures.To insure that the Short Distractor remains in place until its removalis desired, various embodiments of the Short Distractor are availablewith varying degrees of resistance to dislodgment. In the preferredembodiment of the procedure, attention is then directed to thecontralateral side of the spine.

[0162] Step 4. On the contralateral side of the same interspace the LongDistractor having at its working end the diameter matching the ShortDistractor already in place, is then inserted. If however, due to anasymmetrical collapse of the interspace it is then determined thatgreater distraction is required on the second side to achieve theoptimal stability, then the appropriate Short Distractor would be placedon the second side. Then the Short Distractor would be removed from thefirst side and replaced with a larger Long Distractor so as to bring theinterspace into balance.

[0163] In an alternative embodiment, the entire procedure is performedon the one side of the spine utilizing only the Long Distractor prior torepeating the procedure on the contralateral side of the spine. Whilethis method can be performed in accordance with the remaining steps asdescribed in the preferred embodiment, when utilized it is bestperformed using a Trephine which allows the Long Distractor to remain inplace, thereby allowing for interspace distraction otherwise provided inthe first method by the Short Distractor. This alternative method thenrequires the use of a Trephine over the Long Distractor in lieu of areamer and is therefore called the “Trephine Method”, which will bediscussed in detail later.

[0164] Step 5. With the Short Distractor in place on the first side ofthe spine, and the matching Long Distractor in place on the second sideof the spine, and with the dural sac and traversing nerve root safelyretracted, the Outer Sleeve is placed over the Long Distractor andfirmly impacted to its optimal depth using the Impaction Cap and amallet. The Long Distractor is then removed.

[0165] Step 6. An Inner Sleeve is then placed within the Outer Sleeve,and the interspace is then prepared on that side by utilizing a Drill,Endmill, Reamer, or Trephine to drill, ream, or cut out the bone to beremoved to either side, as well as any remaining interposed discalmaterial. In the preferred method, utilizing a specially designedEndmill-Drill, it and the Inner Sleeve are removed as a unit, safelycarrying away the bone and disc debris trapped within them from thespinal canal.

[0166] Step 7. If required, a thread forming Tap with penetrationlimiting means to control the depth of insertion, is then insertedthrough the Outer Sleeve.

[0167] Step 8. The prepared implant is then inserted utilizing thespecialized Driver unit. It should be noted that the implant may becoated with, made of, and/or loaded with substances consistent with bonyfusion. However, in the preferred embodiment, the implant is treatedwith bone promoting and inducing substances, but is loaded withmaterials suitable for participating in a fusion.

[0168] While substances both natural and artificial are covered by thepresent invention, the preferred embodiment is in regard to the use ofthe patient's own bone by the following method. A hollow Trephine isutilized to harvest a core of bone from the posterior superior aspect ofthe iliac crest adjacent the sacroiliac joint. This core of bone is atits outside diameter, slightly smaller than the inside diameter of thespinal implant to be loaded, but longer than the spinal implant.Utilizing an instrument designed for that purpose, the core of bone isthen injected from within the Trephine into the central cavity of theimplant causing a superabundance of the bone material within the implantsuch that the bone material tends to press out through the openingscommunicating with the outside surface of the implant.

[0169] Step 9. Using the Driver Extractor instrument, the preparedimplant is threaded into the prepared interspace. The instrumentation isremoved from that side of the spine and attention is then redirected tothe first side of the spine. A small retractor is utilized to move thedural sac and traversing nerve root medially and to protect them andallowing the direct visualization of the retained Short Distractor unit.Without removing the Short Distractor, it is reassembled to its shaftportion, essentially reconstituting itself into a Long Distractor. Withthe inserted implant now acting as the distractor on the opposite side,the Long Distractor is utilized to guide the Outer Sleeve down where itis impacted as described in Step 5.

[0170] Steps 6 & 7 are then repeated, completing the procedure at thatlevel. The wound is then irrigated and closed in the routine manner.

REPRESENTATIVE EXAMPLE OF THE PREFERRED METHOD

[0171] Through preoperative templating of the patient's anteriorposterior, lateral, and axially imaged MRI scan in conjunction withtranslucent overlays of the various sized implants, the correct implantdiameter and length are accurately assessed, as well as the correctamount of distraction needed to restore the interspace to its premorbidheight. The patient is then properly positioned and a bilateral partialdiscectomy performed via paired semihemilaminotomies.

[0172] For the purpose of this example, it will be assumed that bypreoperative assessment it was determined that the correct implant wouldhave an external diameter of 18 mm and be 26 mm long. Further, thedistraction necessary to restore the height of the interspace would beapproximately 10 mm. The dural sac and traversing nerve root would thenbe retracted medially and protected, while a Long Distractor having anoutside diameter to the barrel portion corresponding to the implant tobe inserted, that is 18 mm, and having a diameter at the working end ofperhaps 8 mm, would be inserted. This then being found to be slightlysmaller than optimal by direct observation, a Convertible Distractorhaving in its barrel portion an 18 mm outside diameter, but having inits working portion a 10 mm diameter would then be inserted. Directobservation and/or x-ray then confirming the ideal distraction, theConvertible Distractor would then be disassembled, the barrel and headportion removed, and the Short Distractor portion left deeply embeddedand with its flanged head flat against the canal floor and deep to theneural structures. It would then be safe to allow the dural sac andnerve root to return to their normal positions, which would besuperficial to the flanged portion of the Short Distractor.

[0173] Attention would then be directed to the contralateral side. Thedural sac and nerve root would then be retracted medially on this secondside, and a Long Distractor with an 18 mm diameter barrel portion and a11 mm working portion would then be inserted into the interspace anddriven flush to the bone if necessary, such impaction imploding anyosteophytes not already removed, and assuring that the shoulder portionof the barrel comes to lie flat against the posterior aspects of theadjacent bodies. With the dural sac and nerve root still safelyretracted, the Outer Sleeve would then be placed over the LongDistractor and utilizing the Driver Cap and a mallet, seated to theoptimal depth.

[0174] In the preferred embodiment, the Long Distractor is then removedand the Inner Sleeve is inserted into the Outer Sleeve. Since thepurpose of the Inner Sleeve is to support the drill and allow for theincreased size of the implant over the size of the drill, thus making itpossible for the insertion of the implant to occur through the OuterSleeve, the Inner Sleeve therefore measures 18 mm in its outsidediameter, and 16.6 mm in its inside diameter. This allows it to fitwithin the Outer Sleeve, the diameter of which is 18.1 mm and to admitthe drill bit which is 16.5 mm in diameter.

[0175] Following the drilling procedure, the Drill and Inner Sleeve areremoved as a single unit with the trapped interposed cartilaginous andbony debris. The depth of drill penetration is preset and limited by thefixed rigid column of the Outer Sleeve. In this example, the space willbe prepared to a depth of 28 mm in anticipation of countersinking a 26mm long implant at least 2 mm. If a Tap were to be utilized, it would beinserted at this time and be appropriate to the minor and majordiameters of the implant to be inserted and as with the Drill,controlled for its depth of penetration. The spinal implant would thenbe prepared for implantation by utilizing a Trephine to harvest a coreof posterior iliac bone greater than 30 mm long and approximately 14.5mm in diameter.

[0176] Using the Bone Loading Device, this core of bone would beforcefully injected into the internal chamber of the spinal implantwhich would then be capped. Cap end forward, the fully loaded implantwould then be attached to the Insertion Driver, down the Outer Sleeveand screwed into place with the depth of penetration limited by theInsertion instrument. The Insertion Driver is then unscrewed from theimplant and removed from the Outer Sleeve. With the dural sac and nerveroot retracted and protected, the Outer Sleeve would then be removed.This would complete the fusion procedure on that side, and then asdescribed, the procedure would be repeated on the other (first) side ofthe same interspace.

[0177] Alternative Methods

[0178] An alternative and extremely useful method is the “TrephineMethod”. Its advantages include that it may be used in conjunction withthe preferred embodiment substituting the use of a hollow, tubularcutter, called a Trephine for the use of the Drill in Step 5 of thepreferred embodiment. Additionally, it may be utilized so as to obviatethe need for the placement of the Short Distractor and to allow theprocedure to be effectively performed from start to finish on one sideprior to initiating the procedure on the opposite side, and whilenevertheless maintaining distraction at the site of the bone removal.

[0179] The following is a description of the “Trephine Method”. Havingcompleted the exposure of the interspace on at least one side, the duralsac and nerve root are retracted. A Long Distractor differing from theLong Solid Bodied Distractor of the preferred embodiment only in thatthe barrel portion is of a precisely lesser diameter than the spinalimplant. As in the preferred embodiment, the Outer Sleeve has an innerdiameter only slightly greater than the implant to be inserted.Therefore, at this time, a first Inner Sleeve is inserted into the OuterSleeve to make up the difference between the outside diameter of theLong Distractor and the inside diameter of the Outer Sleeve. With theOuter Sleeve and first Inner Sleeve thus assembled, they are placed overthe Long Distractor and the Outer Sleeve is optimally seated using theImpaction Cap. The Cap and first Inner Sleeve are removed, but the LongDistractor and Outer Sleeve are left in place.

[0180] With the Long Distractor maintaining optimal distraction and withthe Outer Sleeve locking the vertebrae together so as to resist anymovement of the vertebrae, a hollow, tubular cutter known as a Trephineis then inserted over the Long Distractor and its barrel portion andwithin the Outer Sleeve. The Trephine, which is stopped out to theappropriate depth, can then be utilized to cut equal arcs of bone fromthe opposed vertebral endplates.

[0181] Alternatively, a second Inner Sleeve may be placed within theOuter Sleeve prior to placing the Trephine over the Long Distractor andwithin that second sleeve. This second Inner Sleeve would be justgreater in its internal diameter than the Long Distractor and justsmaller in its outside diameter than the inner diameter of the OuterSleeve. While it would provide enhanced stability to the Trephine,provision would then need to be made in is the way of large flutespassing longitudinally or obliquely along the outer surface of theDistractor to its barrel portion to accommodate the bony andcartilaginous debris generated during the cutting procedure.

[0182] Following the use of the Trephine to the appropriate depth byeither of these methods, the Trephine, the Long Distractor, and thesecond Inner Sleeve, if utilized, are all removed. Since the Trephinecuts two arcs of bone but does not ream them out, a shafted instrumentwith a perpendicular cutting portion at its working end is then insertedparallel to the disc space and then rotated through an arc of motioncutting the bases of the two longitudinally cut arcs, thus freeing themfor removal through the Outer Sleeve. The space may then be tapped ifrequired, and the implant is inserted as per the preferred method. Asalready mentioned, the “Trephine Method” can be used with or without theuse of the Short Distractor on the contralateral side.

[0183] Applications of Method in other Areas of the Spine

[0184] The following method is the preferred embodiment for performinganterior interbody fusion in the thoracic and lumbar spines. It is alsoappropriate in the cervical spine when the width of the spine anteriorlyis sufficient so that it is possible to place two implants side by sideand such that each intrudes at least several millimeters into thesubstance of the opposed vertebrae and for the length of the implants.

[0185] The interspace to be fused is adequately exposed and the softtissues and vital structures retracted and protected to either side.Visualization of the broad width of the interspace anteriorly is madepossible by the absence of the neurological structures in relation tothis aspect of the spine. The center line of the anterior aspect of theinterspace is noted and marked. The disc is removed using first a knifeand then curettes and rongeurs as needed. Alternatively, the disc may beleft intact to be removed during the drilling stage of the procedure.However, as per the preferred embodiment of the procedure, havingremoved the great mass of the nucleus and the greater portion of theannulus anteriorly, Long Distractors with progressively increasingdiameters to their working ends are inserted into the interspace at apoint midway between the central marking line and the lateral extent ofthe anterior aspect of the spine as visualized.

[0186] The Dual Outer Sleeve with its common Foot Plate and RetentionProngs is then inserted over either a singly placed Long Distractor andthen the second Distractor placed, or is placed over both Distractors ifalready placed. The Dual Outer Sleeve is then seated firmly against theanterior aspect of the spine. Any spurs which would interfere with theflush seating of the Foot Plate to the anterior aspect of the spineshould be removed prior to inserting the Long Distractors. Once theOuter Sleeve has been optimally seated, one of the Long Distractors isremoved and in its place is inserted an Inner Sleeve and drill bit. Thedrill bit has as its outside diameter the minor diameter of the implantto be inserted. The Inner Sleeve is essentially equal in thickness tothe difference between the minor and major diameters of the threadedimplant.

[0187] A Stopped Drill is then utilized to prepare the opposed vertebralsurfaces and to remove any remaining disc material interposed. Ifrequired, a Stopped Tap may be inserted through the Outer Sleeve andinto the interspace to create a thread form. The properly preparedimplant is then affixed to the Insertion Driver and passed through theOuter Sleeve down into the interspace and inserted until its depth ofpenetration is limited by the stop on the Insertion Driver. With theimplant itself now in a position to act as a distractor, the LongDistractor is then removed from the contralateral side and the procedurerepeated. When both implants are firmly in place, the outer sleeve maythen be removed. The amount of countersinking of the implants may thenbe adjusted under direct vision.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT METHOD ANDINSTRUMENTATION

[0188] In the preferred embodiment, the disc (D) between adjacentvertebrae (V) is approached via bilateral paired semihemilaminotomies ofthe adjacent vertebrae. In the preferred embodiment the supraspinousligament, the interspinous ligament, the spinous process, portions ofthe lamina, and most of the facet joints are preserved. However, whileless desirable, these structures may be removed.

[0189] In the preferred method, a bilateral partial nuclear discectomyis then performed through bilateral openings created through theposterior aspect of the annulus fibrosus. While considered lessdesirable, disc excision can be delayed and performed simultaneouslywith the vertebral bone resection during the drilling procedure.Starting on the first side a dural nerve root retractor is placed suchthat the dural sac and lower nerve root are retracted medially allowingexposure to one side of a portion of two adjacent vertebral bodies andthe interposed disc posteriorly.

[0190] Referring now to FIG. 1, preferably after removing some portionof nuclear disc material, a Long Distractor 100 is inserted under directvision into the intervertebral space. The disc penetrating portion 102is essentially cylindrical with a bullet-shaped front end 103 and ashoulder portion 104 where the penetrating portion 102 extends frombarrel 106. The penetrating portion 102 urges the vertebral bodiesapart, facilitating the introduction of the instruments. LongDistractors with sequentially increasing diameter penetrating portions102 are then introduced. As the optimal diameter of penetrating portion102 is achieved, the vertebral bodies to either side are forced intofull congruence and thus become parallel, not only to the penetratingportion 102, but to each other. At this time, any remaining excrescencesof bone of the posterior vertebral bodies adjacent the posterior discwhich have not already been removed are flattened flush to the vertebralbody by the forced impaction, such as by hitting with a hammer flatsurface 109 of crown 110, driving the shoulder 104 against the lippedportions of vertebrae V. Because of the forced opposition of thevertebral endplates to portion 102 with optimal distraction, unit 100will then come to lie absolutely perpendicular to the plane of theposterior bodies and absolutely parallel to the vertebral endplates,allowing optimal alignment for the procedure to be performed.

[0191] Penetrating portion 102 is available in various diameters, butall are of a constant length, which is less than the known depth of theinterspace. This combined with the circumferential shoulder 104, whichis too large to fit within the interspace, protects against the dangerof overpenetration. Barrel 106 is of the same diameter as the externaldiameter of the device to be implanted. A recessed portion 108 below thecrown 110 allows for the Long Distractor 100 to be engaged by anextractor unit shown in FIG. 9.

[0192] In the preferred embodiment, a Convertible Long Distractor 113 isused on the first side of the spine. As shown in FIG. 2, the ConvertibleLong Distractor 113 has a barrel portion 152 separable from the ShortDistractor portion 120. While the initial distraction may be performedwith a solid Long Distractor, as the optimal distraction is approachedthe appropriate Convertible Long Distractor is utilized. The ConvertibleLong Distractor 113 consists of a Short Distractor portion 120 and abarrel 152 having a rectangular projection 134 at one end. The ShortDistractor 120 has an increased diameter head 128, a rectangular slot118 and an internal threaded opening 114. The barrel 152 is hollow andhas an internal shaft 111 terminating in a large diameter hexagonalcrown 115 at one end and a reduced diameter portion 112. The crown has adetent portion 117 in its flat surface. The other end of the shaft 111has a threaded small member 116 that corresponds to threaded opening114. The shaft 111 is prevented from removal from the barrel 152 by setpin 119 passing through the wall of barrel 152 in a convenient manner.The Short Distractor portion 120 is removably attached to the barrelportion 152 via the mating of female rectangular slot 118 and the malemating member 134. The mating held together by utilizing is knob 136 todrive the crown 110 connected to interior shaft 111 having a threadedworking end screw 116 that threads into the female aperture 118 of theShort Distractor portion 120.

[0193] Cap 136 has an open socket 138 for fitting around crown 115 andengages the reduced diameter hexagonal portion 112 so as to permit therotation of shaft-111 and threaded male member 116. A detent ball 150 inthe inside of the socket 138 engages detent 117 in the crown 115,holding them together.

[0194] The Short Distractor portion 120 of FIGS. 2, 3, and 3A-3F aredesigned to provide for high stability when temporarily situated so asto resist inadvertent migration while the surgeon is working on thesecond side. To that end, the embodiment of the Short Distractor 120shown in FIGS. 3 and 3A has a pair of sharp pegs 126, to embed into theopposing vertebral bodies and forward facing ratchetings 124, thatfurther resist backward movement. FIGS. 3B and 3C, which show thepreferred embodiment, are side and top views of an alternativeembodiment of the distractor portion such that the distractor portion tobe interposed between the vertebrae is essentially cylindrical, but withcircumferential forward facing ratchetings 124.

[0195] A further alternative embodiment is shown in FIGS. 3D and 3E.This is a more rectangularized design, with forward facing ratchetings,without the sharp prongs 126 of FIG. 3. FIG. 3F is a side view of afurther embodiment of the Short Distractor 120 shown with knurling, toincrease the interference with the bone surface so as to add stabilityto the unit and to resist dislodgment. To this end, it is apparent thatthe working ends of both the Long and Short Distractors can have avariety of configurations consistent with their purpose, and thatsurface irregularities as well as the shape of the ends themselves, withor without prongs 126, may be utilized to make the Short Distractor 120more resistant to migration.

[0196] Once the ideal distraction has been achieved on the first side ofthe spine, the Convertible Distractor is dissociated, leaving ShortDistractor 120 in place with its rounded external end 128, safely on thecanal floor and deep to the dural sac and nerve root.

[0197] As shown in FIG. 4, the surgeon then moves to the other side ofthe spine at the same disc (D) level, and retracts the dural sac andnerve root medially, exposing the disc on that side. Long Distractors100 are then sequentially inserted into the disc space until thediameter of the distractor on the second side is at least as big as thaton the first side. If because of some asymmetry of the interspace alarger diameter distractor is required on the second side to achieve theideal distraction as compared to the first side, then the second side isfitted with a Short Distractor of the larger diameter, and the surgeonwould then return back to the first side. In that event, the first sideShort Distractor would then be removed and the Long Distractor 100corresponding to the increased diameter of the already placed ShortDistractor 120 would then be inserted. In either event, the operation iscontinued by working on the one side where the Long Distractor is inplace. In this regard, it should be noted, that by the use of such adevice as the Michelson Spinal Surgery Frame, it may be possible toobtain adequate distraction preoperatively such that the surgeon iseither disinclined to use a distractor, or to simply place the correctLong Distractor on the first side and then proceed with the surgicalprocedure on that side before moving to the opposite side. Thesevariations are within the scope of the present invention.

[0198] The Long Distractor now serves as both a centering post and analignment rod for the hollow Outer Sleeve 140 shown in FIG. 5 which isfitted over the Long Distractor 100, shown by phantom lines 101 in FIG.5. The Outer Sleeve 140 is metal and has a sharp toothed front end 142that is capable of penetrating into and holding fast the two adjacentvertebrae (V). Interrupting the circumferential sharp teeth of 142 areflat, planar areas 152 which serve to resist the further insertion ofthe sharp teeth into the vertebral bodies. The toothed front end 142 ofthe Outer Sleeve 140 is a continuation of the tubular shaft 144, whichin turn is connected to circumferentially enlarged tubular back end 146having a knurled outer surface 148 for easier manipulation. Analternative embodiment of an Outer Sleeve incorporates an expansile keyhole and slot configuration 154 to either side of shaft 144 along themid-plane of the interspace and parallel to it such that the end 142resists the collapse of the vertebrae (V) to either side of the disc(D), but may nevertheless allow for their further distraction, in theevent the only diameter or the root diameter of the implant is largerthan the hole drilled.

[0199] A Driver Cap 160 in-the form of an impaction cap has at its farend a flat, closed-back surface 162 and at its other end a broad,circular opening. The Driver Cap 160 fits over both the Outer Sleeve 140and the Long Distractor 100. As the Driver Cap 160 is seated, interiorsurface 170 circumferentially engages portion 146 of the Outer Sleeveuntil the back end 172 engages the internal shoulder 164. As malletblows are applied to surface 162, that force is transmitted via theinternal shoulder 164 to the Outer Sleeve 140 via its far end 172,seating teeth 142 into the vertebral bodies adjacent the disc space Dand to the depth of the teeth 142 to the flat portions 152. As the OuterSleeve 140 is advanced forward, crown portion 110 of the Long Distractoris allowed to protrude within the Driver Cap 160 unobstructed until itcontacts the interior flat surface 168. Once crown 110 comes intocontact with the flat interior surface 168, then further taps of themallet will not advance the Outer Sleeve, any further motion beingresisted by the flat shoulder portion 104 of the Long Distractorabutting the hard surfaces of the posterior vertebral bodies. In thisway, the Outer Sleeve 140 is safely and assuredly inserted to itsoptimal depth and rigidly securing the two opposed vertebrae as shown inFIG. 6.

[0200] The Cap 160 is then removed and the Distractor Puller 200 of FIG.9 utilized to remove the Long Distractor 100 from the spine leaving theOuter Sleeve 140 in place. The Distractor Puller 200 has front portion202, a mid portion 204, and a back handle portion 206. At the frontportion 202 of the Distractor Puller 200, a socket 208 is connected toone end of shaft 210 which at its far end is connected to back handleportion 206. The socket 208 has defined within it a cavity 212 that isopen at its front end and funnelized on the interior aspect of itssides. The cavity 212 is constructed so that the head of the DistractorPuller 200 and the partially circumferential flange 218 engages thecircumferential recess 108 of the Distractor 100. The entrance to cavity212 is slightly funnelized, and the leading edges of flange 218 slightlyrounded to facilitate the engagement of recess 108 and head 110 ofDistractor 100, which is further facilitated in that the Driver Cap 160leaves portion 108 of Distractor 100 precisely flush with the backsurface 172 of the Outer Sleeve 140. This provides a large, flat surface172 to precisely guide surface 230 of socket 208, and open portion 212around head 110 while flange 218 engages recess 108. The springloadeddetent ball 228 engages hemispherical depression 112 in the crown 110,shown in FIG. 2. This springloaded detent 228 in engagement withcomplimentary indent 218 protects against the inadvertent dissociationof the Long Distractor from the Puller 200 after the Distractor has beenremoved from within the Outer Sleeve 140 and prior to its removal fromthe wound. Once out of the body, the two instruments are easilydisassociated by freeing the crown portion 110 from cavity 212 by amanual force applied perpendicular to their relative long axes at thislocation.

[0201] A cylindrical and free removable weight 216 is fitted aroundshaft 210 between the front portion 202 and the rear handle portion 206.Gently, but repeatedly sliding the weight 216 along shaft 210 and drivenrearwardly against flat surface 228, transmits a rearward vector toproximal end 202 and thereby to the Long Distractor 100 to which it isengaged.

[0202] Paired extended handle 224 and 226, allow the surgeon to resistany excessive rearward motion as the instrument is used to liberate theLong Distractor 100. Paired handles 224 and 226 are also useful in thatthey allow a rotational directing of portion 208, via the shaft 210.This allows the surgeon to control and manipulate rotationally theorientation of the opening of cavity 212 to facilitate its application,to the head 110 of the distractor 100.

[0203] The Distractor Puller 200 is a significant improvement over thealternatives of striking a remover instrument with an independent hammerover the exposed surgical wound, or manually extracting the distractorby forcefully pulling. The use of a free hammer over the open wound isdangerous because the neural structures can be impacted on the backswing which is made even more likely by the effects of gravity on themallet head. Manual extraction by pulling is dangerous because of thesignificant interference fit of portion 102 within the spine such thatsignificant force would be required to remove the Distractor 100, and ifforce were not coaxial then the Outer Sleeve might be dislodged ormisaligned. Further, once the flat portion 102 became free of theinterspace, all resistance to withdrawal would be lost and in the faceof the considerable force necessary to free it, the Distractor 100 mighteasily become projectile imparting injury to the patient and/or thesurgeon.

[0204] Once the Long Distractor 100 has been fully removed from theOuter Sleeve 140, the toothed end 142 of the Outer Sleeve 140, workingin conjunction with the Short Distractor 120 on the contralateral siderigidly maintains the relative position of the adjacent vertebrae V.Further, since the remainder of the procedure on that side of the spineoccurs entirely through the protective Outer Sleeve 140, and as thenerves and dural sac are external to that Outer Sleeve and superficialto the toothed end 142 of the Outer Sleeve 140, which is firmly embeddedinto the adjacent vertebrae V, the Outer Sleeve 140 serves to insure thesafety of these delicate neural structures. Further, since the OuterSleeve 140 is of a fixed length and rigid, its flat rearward surface 172may be used as a stop to the advancement of all instruments placedthrough the Outer Sleeve 140, thus protecting against accidentaloverpenetration. Further, the Outer Sleeve 140 assures that the furtherprocedure to be performed will occur coaxial to the disc space D andfurther, be symmetrical in regard to each of the opposed vertebralsurfaces.

[0205]FIG. 10B is a posterior view of the spine at this stage of theprocedure, showing a Short Distractor 120 in place on one side ofthe,spine and the bottom portion of Outer Sleeve 140 in place on theopposite side of the spine.

[0206] Referring to FIG. 11A, an Inner Sleeve 242 is inserted from therear within the Outer Sleeve 140. This Inner Sleeve has a collar portion244 of a known thickness which seats against the top edge surface 172 ofOuter Sleeve 140. The cylindrical barrel portion of Inner Sleeve 242comes to approximate the posterior aspect of the vertebral bodiesinterior the Outer Sleeve when fully seated. A Drill 240, having a knownselected length is then introduced through the rearward aperture of theInner Sleeve 242 and utilized to ream out the arcs of bone which itengages from the opposed vertebral endplates as well as any discalmaterial within its path down to its predetermined and limited depth.The Drill 240, has a narrow engagement portion 246, which allows it tobe affixed to a drill mechanism which may be either a manual or a powerunit. A circumferential collar 248 of an increased diameter serves tolimit the depth of penetration of the drill 240 and may be fixed, orlockably adjustable.

[0207] Not shown here, but well known to those skilled in the art, arevarious mechanisms to lockably adjust such instruments as drills. Suchmechanisms include, but are not limited to, the use of collets, threadedshafts with lock nuts, and flanges engaging grooves forced therein byeither a cap pulled over the flanges or screwed down upon them.

[0208] In the preferred embodiment, the forward cutting edge 252 ofDrill 240 is a modification of a large fluted drill design such that theend resembles an end cutting mill which may contain any workable numberof cutting surfaces, but preferably four or more, and such cuttingsurfaces being relatively shallow such that the advancement of theinstrument occurs more slowly. The outside diameter of the Drill 240corresponds to the minor diameter of the threaded spinal implant. TheInner Sleeve 242 has an inner diameter slightly greater than thatdimension and its outer diameter is slightly smaller than the insidediameter of the Outer Sleeve 140 which has the same outer diameter asthe major diameter of the threaded implant.

[0209] The drill shaft of drill 240 comprises an upper portion 243, acentral recessed portion 256 of a smaller diameter and a lower cuttingdrill portion 250. The upper portion 243 and lower portion 256 of thedrill 240 have the same outside diameter.

[0210] The Inner Sleeve 242 serves many functions. First, it provides amore intimate drill guide for drill 240 in the event a smaller diameterhole is to be drilled than that of the inside diameter of the OuterSleeve 140. Second, since it now guides the Drill, it allows for theOuter Sleeve 140 to have an internal diameter large enough to admit thethreaded spinal implant, which is indeed considerably larger in diameterthan the Drill 240 itself.

[0211] If a larger Outer Sleeve 140 were utilized absent the InnerSleeve 242, then the Drill 240 would be free to wander within theconfines of that greater space and would not reliably make parallel cutsremoving equal portions of bone from the adjacent vertebrae V. Further,the bone removal not only needs to be equal, but must be correctlyoriented in three dimensions. That is, the path of the Drill 240 must beequally centered within the disc space, parallel the endplates, andparallel to the sagittal axis dissecting the interspace.

[0212] A further purpose of the Inner Sleeve 242 is that it may beremoved simultaneously with the Drill 240, thereby trapping the debris,both cartilaginous and bony generated during the drilling procedure,which are guided rearward by the large flutes 251 of Drill portion 250,where they are collected around recessed portion 256 between therecessed portion 256 and the inner wall of the Inner Sleeve 242 arethere contained therein. Thus, by removing the Drill 240 in conjunctionwith the Inner Sleeve 242, all of the debris generated by the reamingprocedure is safely removed from the spinal canal and wound area.

[0213] Further, if the disc tissue in the area to be reamed has beenremoved previously, as per the preferred method, then the patient's ownbone of good quality and useful within the operation will then becontained between the Inner Sleeve 242 and the shaft portion 256. Onceaway from the surgical wound, this material may be used to load thespinal implant or placed deep within the interspace to participate inthe fusion.

[0214] The method of actually producing the surgical hole within thespine is variable. As shown in FIG. 1C, in an alternative embodimentDrill end 250 has a forward projecting nipple 260, which itself isbullet-shaped in its leading aspect so as to ease its entrance into thedisc space and to urge the vertebrae apart. Nipple 260 is distracting,stabilizing as it resists any tendency of the vertebrae to movetogether, is self-centering to the Drill portion 250 when working inconjunction with Sleeves 140 and 242, and virtually assures thesymmetrical resection of bone from the opposed vertebral surfaces.

[0215] The alternative “Trephine Method” referred to earlier in thisapplication, is shown in FIG. 11B. In this alternative, a LongDistractor 100 is left in place after the Outer Sleeve 140 is seated.The Long Distractor 100 in this case differs from the Long Distractor ofthe preferred embodiment in that its outside diameter of the barrel 106is of a smaller diameter than in the prior version. This is madenecessary because regardless of the method, the hole to be formedcorresponds to the minor diameter of the spinal implant. Trephine 270, ahollow, tubular member with sharp cutting teeth 251 at its proximal end,has a wall thickness and since the outside diameter of that trephine 270must correspond to the root diameter of the implant, then the wallthickness of the trephine 270 must be allowed for by a correspondingreduction in the diameter of the Long Distractor 100.

[0216] A further modification of the Long Distractor 100 to the“Trephine Method” would use longitudinal grooves (not shown) along thebarrel surface 106 for the purpose of transmitting any debris generatedduring the cutting procedure, rearward. Since the cutting element isboth centered and aligned by the Long Distractor, the use of the InnerSleeve 242 is not mandatory, but may once again be useful in controllingthe path of the debris. To that end, little debris is generated in the“Trephine Method” as the bony arcs are not so much being reamed out andremoved as they are simply being cut into the bone where these arcs ofbone are left connected at their far ends. Thus, when the TrephiningMethod has been completed and the Trephine 270 and Inner Sleeve 242removed, unlike in the preferred embodiment where the hole is drilledout, it remains necessary to remove both the two arcs of bone, and anyinterposed material. Nevertheless, this is very easily performed byvarious means, one of which is depicted in FIG. 11D.

[0217] Instrument 272 consisting of a shaft 276 attached off center tothe lower surface 273 handle 274. The shaft 274 terminates in a cuttingarm 278. The instrument 272 is inserted through Outer Sleeve 140 wherethe lower surface 273 of handle 274 abuts the top 172 of the OuterSleeve 140, both stopping downward motion of instrument 272 andprecisely placing the perpendicularly cutting arm 278 of instrument 272so that as handle portion 274 is rotated, the cutting arm 278 is alsorotated, cutting the arcs of bone and liberating them from their lastattachments. These portions of bone are then removed utilizing thisinstrument or a long forceps, and then placed within the implants orotherwise used to participate in the fusion.

[0218] While in the preferred embodiment of the present invention thespinal implant I, is essentially self-tapping, if the bone is unusuallyhard it may be desirable to form the thread pattern within theinterspace prior to the insertion of the implant I. To that end, asshown in FIG. 12, Tap 280 has a thread-cutting portion 282 connected bya shaft 286 to a handle portion 292, which has been designed to givemechanical advantage to the rotation of the instrument for the purposeof cutting threads. The lower portion of handle 290 has a forward facingflat surface 288 too large to fit through the opening of Outer Sleeve140 which thus safely limits the depth of penetration of the cuttingelement 282. This tap 280 is further made safe by blunt end 294 whichwill engage the uncut portions of the vertebral bone just prior to theengagement of shoulder 288 against surface 172. This feature allows thesurgeon to appreciate a less harsh resistance as the blunt nose 294encounters the remaining unresected bone for the drill hole and prior tothe sudden increase in resistance caused by the seating of shoulder 288against top edge 172, which first resistance serves as a warning to thesurgeon to discontinue the tapping procedure. Thus, the surgeon has bothvisual (as shoulder 288 approaches top edge 172) and tactile warnings toavoid stripping the thread form. Tap end 282 is highly specialized forits specific purpose. Rearward to the specialized blunt tip 294 is atruncated bullet-shaped area 298 which ramps up to the constant diameterintermediate the cutting ridges 296. Ramp portion 298 urges the opposedvertebral bodies apart, which motion is resisted by Outer Sleeve 140,thus progressively driving the sharp leading edges of thread forms 296into the vertebral bodies. The periodic longitudinal grooves 284interrupting the thread forms, which may number 1 to 8, but preferably4, function to accumulate the bony material which is removed during thethread cutting process. In that regard, in the ideal embodiment, thethread cutting form is designed to compress the bone to be formed ratherthan to trough through it. Further, while both the major and minordiameters of the Tap 280 may be varied, in the preferred embodiment, theminor diameter corresponds to the minor diameter of the implant I, butthe major diameter is slightly less than the major diameter of theimplant.

[0219] With Tap 280 now removed, and Sleeve 140 still in place, thesurgical site is now fully prepared to receive the spinal implant I. Inthe preferred embodiment of the spinal implant, the implant has beenenhanced by the use of, application to, and filling with fusionpromoting, enhancing, and participating substances and factors. Thus,the implant may be fully prepared for insertion as provided to theoperating surgeon. However, at the present time, human bone is mostcommonly used as the graft material of choice, with the patient's ownbone being considered the best source.

[0220]FIG. 14a shows a trephine 300 with an exceedingly sharp frontcutting edge 302 for quickly and cleanly coring into the patient'sposterior iliac crest, or any other bony tissue, and for the purpose ofproducing a core of bone then contained within the hollow 304 of thetrephine 300. Trephine 300 has a rear portion 306 with a pair ofdiametrically opposed slots 310, and disposed clockwise from theirlongitudinally oriented rearward facing openings so as to engagediametrically and opposing members 312 of Drive unit 308, by whichtrephine 300 may be attached to either a hand or power drill. It can beappreciated that engagement mechanism 312 is stable during the clockwisecutting procedure, and yet allows for the rapid disconnection of the twocomponents once the cutting is completed.

[0221] Because of the high interference between the graft and the innerwall of hollow portion 304, and the relative weakness of the cancellousbone being harvested, it is possible to remove the Trephine 300 whilestill drilling, and to have it extract the core of bone with it.However, in the highly unlikely event that the core of bone would remainfixed at its base, then with the drive mechanism 308 removed, acorkscrew 408 shown in FIG. 14C is introduced though the central openingof rear portion 306 and threaded down and through the core of bonewithin 304 and to the depth of teeth 302. The tip 318 of the corkscrew408, which extends substantially on line with the outer envelope of thecorkscrew, then cuts radially through the base of the bone core. As thehandle portion 314 of the corkscrew 408 abuts the flat, rearward surfaceof portion 306 and it can no longer advance. As corkscrew 408 iscontinued to be turned further, it will cause the core of bone to bepulled rearward, as in removing a cork from a wine bottle. Trephine 300has a barrel portion 304 continuous with sharp toothed portion 302having an inner diameter just less than the inner diameter of the spinalimplant I to be loaded.

[0222] The Trephine 300 with its core of harvested bone is then placedas shown in FIG. 14B, through opening 340 of Implant Bone Loading device320, where the barrel portion 304 then passes through and is stopped bycircular flange 344. The plunger shaft 326 of instrument 320 is thenprepared for attachment by rotating knob 332 counterclockwise such thatthe plunger 372 is pulled via the long threaded shaft portion 328 backto the base of collar 330 at its proximal end. In this position, knob332 is considerably extended rearward from collar 330. With plungershaft 326 in this position, the plunger head 372 is inserted into thecentral hollow of portion 306 of Trephine 300 as the proximalcylindrical portion of collar 330 then follows it, such that the plunger372 then occupies the rearward portion of barrel 304 and the proximalcylindrical portion of collar 330 occupies the central hollow of portion306. A pair of diametrically opposed radially projecting arms 346 oncollar 330 are then advanced longitudinally into diametrically opposedpaired L slots 340 and then rotated clockwise to complete this assembly.

[0223] At the other end of instrument 320, a spinal implant I is engagedthrough its female rectangular slot 364 by a rectangular protruding barextending from rearward facing surface of end plug 324, (not shown) andsecured there by knob 334 which extends as a rod through a centralaperture within end plug 324 to extend at the far end as a small boltwhich threads to a female aperture centered within the female slot 364of the spinal implant. With the spinal implant I secured to end plug 324and the opposite end of the implant I presenting as a hollow, tubularopening, end plug 324 is advanced into device 320 where it is secured byrotationally engaging diametrically opposed L-shaped slots 321. Withdevice 320 fully assembled, end 302 of trephine 300 lies coaxial andopposed to the open end of implant I.

[0224] As shown in FIG. 15, as knob 332 is then rotated clockwise, theplunger 372 proximal the threaded shaft 328 is then forcibly, butcontrollably driven forward down the barrel 304 ejecting the bone graftdirectly into the spinal implant I. As the bone graft is greater inlength than the interior of the spinal implant, with further compressionthe bone is forced into the radially disposed apertures through the wallof the device communicating from the central cavity to the exterior.

[0225] End plug 324 is then removed from apparatus 320. Using end plug324 as a handle, end cap 374 shown in FIG. 16 is secured to the open endof the spinal implant I. The implant is then disassociated from end plug324 by rotating knob 334 counterclockwise.

[0226]FIG. 16 shows an Implant Driver instrument which may be used toeither insert or to remove said implant I. Driver 350 has at its far end362, a rectangular protrusion 398, which protrusion intimately engagesthe complimentary rectangular slot 364 of implant I. Protruding fromslot 398 of end 362 is threaded portion 353, which extends as a rodthrough hollow shaft 358 and hollow hand barrel 360 to knob 354 where itcan be rotationally controlled. Threaded portion 353 screws into afemale aperture central slot 364, urging 353 into 364, and binding themtogether such that instrument 350 can be rotated via paired anddiametrically opposed extending arms 366 and in either direction whilemaintaining contact with the implant.

[0227] Affixed to the Driver 350, the implant is then introduced throughthe Outer Sleeve 140 and screwed into the interspace opposed between thetwo prepared vertebrae V until such time as the leading edge of theImplant Cap 374 reaches the depth of the prepared hole at which time itsforward motion is impeded by the bone lying before it which had not beendrilled out. This allows for a progressive feel to the surgeon as theimplant is screwed home.

[0228] As described previously, with the use of the Tap 280, thisterminal resistance to further seating provides significant tactilefeedback to the surgeon. Again, as with the Tap 280, visual monitoringof the depth of insertion of the implant is provided to the surgeon byobserving the progressive approximation of the forward surface 370, ofbarrel portion 360, as it approaches the rearward facing surface 172 ofOuter-Sleeve 140. Nevertheless, a final safety mechanism, when the fulldepth of insertion has been achieved, surface 370 of instrument 350 willabut surface 172 of the Outer Sleeve 140, prohibiting any furtherinstallation of the spinal implant.

[0229] Once the implant has been fully installed, the Driver 350 isdissociated from the implant by turning knob 354 in a counterclockwisedirection. The Driver 350 is then withdrawn from the outer sheath, thenthe Outer Sleeve 140 is removed. This leaves the implant fully installedand inset to the determined depth as shown in FIG. 18.

[0230] Attention is then redirected to the other, or first, side of thespine. A dural nerve root retractor is used to retract the neuralstructures medially, bringing into full view the head 128 of the ShortDistractor 120, lying flush on the canal floor. Utilizing apparatus 152,extended screw portion 116 is inserted into the female threaded portion114 of the Short Distractor 120 as the extended rectangular portion 134of apparatus 152 is engaged to the female rectangular portion 118 of theShort Distractor 120. Then turning rearward facing portions 108 and 110,utilizing the knob 136 of FIG. 2, the Long Distractor configuration isrestored.

[0231] With the dural sac and nerve roots still retracted and protected,the Outer Sleeve 140 is slipped over the reconstituted Long Distractorand seated using the Driver Cap 162. The entire sequence of events asdescribed for the implantation of the spinal implant I as alreadyplaced, is then repeated such that both spinal implants come to lie sideby side within the interspace. Though not necessary, circlage or otherinternal fixation of the levels to be fused may additionally beperformed, and then the wound is closed in the routine manner.

[0232] Brief Discussion with Reference to the Drawings of the PreferredMethod and Instrumentation for Anterior Interbody Fusion IncorporatingIntercorporeal Predistraction and Utilizing a Guarded Sleeve System isDisclosed

[0233] Because of the absence of the spinal cord and nerve roots, it isgenerally possible to visualize in one instance the entire width of thedisc space from side to side throughout the cervical, thoracic, orlumbar spine. In the preferred embodiment of the anterior interbodyfusion, implants are placed side by side from anterior to posteriorparallel to the interspace and extending through into the adjacentvertebral bodies. Where the transverse width of the disc space isinsufficient to allow for the use of two implants, each of which wouldbe large enough to protrude to the required depth into the adjacentvertebrae, then a singular and significantly larger implant may beplaced centrally. With this in mind, and in light of the very detaileddescription of the technique and instrumentation already provided inregard to the method of posterior lumbar interbody fusion, a briefdiscussion of anterior spinal interbody fusion with dual implantinstallation will suffice, and the method for installation of a large,singular midline graft will become obvious.

[0234] The interspace to be fused is exposed anteriorly. The softtissues are withdrawn and protected to either side, and if necessary,above and below as well. It is then possible to visualize the entirewidth of the vertebrae anteriorly adjacent that interspace. As discussedabove, the surgeon has already templated the appropriate patientradiographs to determine the requisite distraction and optimal implantsize. In the preferred method, the surgeon then broadly excises thegreat bulk of the nuclear disc portion. (Alternatively, the disc can beleft to be removed via the drill later.) The surgeon then notes andmarks a point midway from side to side anteriorly. He then inserts LongDistractor 100 centering it on a point midway between the point justnoted and the lateral extent of the intervertebral space visualizedanteriorly. The outer barrel portion 106 of the Distractor 100 utilized,will correspond to the outside diameter of the implants to be installed.The Distractor tips 102 inserted are sequentially larger in diameteruntil the optimal distraction is achieved. This optimal distraction,although suggested by the initial templating, may be visually andtactilely confirmed as performed. When the optimal distraction isachieved, the vertebral endplates will come into full congruence andparallel to the forward shaft portion 102 of the Distractor 100, causingan alteration in the alignment of the vertebrae and a significantincrease in the interference fit and pressurization at the tip, suchthat the instrument becomes exceedingly stable.

[0235] There is a sensation imparted to the surgeon of the tissueshaving moved through their elastic range to the point where the twoadjacent vertebrae V begin to feel and move as if a single solid. Thesechanges are easily appreciated visually as the vertebrae realign tobecome congruent to tip 102, and can also easily be appreciated vialateral Roentgenography. However, should the surgeon fail to appreciatethat optimal distraction has been achieved and attempt to furtherdistract the interspace, he would find that extremely difficult to dobecause of the increased resistance as the tissues are moved beyondtheir range of elastic deformation. Further, there would be noelasticity left to allow the vertebrae to move further apart and thesensation to the surgeon should he attempt to gently tap the oversizedDistractor forward with a mallet, would be one of great brittleness.

[0236] Returning now to the procedure, when the correct intercorporealDistractor 100 producing the ideal interspace distraction having itsbarrel portion 106 corresponding to the implant to be installed has beeninserted, then its exact duplicate is inserted anteriorly equidistant tothe other side of the spine. As the barrel portion 106 of LongDistractor 100 is exactly of the same major diameter as the spinalimplant I looking coaxially on end, the surgeon can then asses theanticipated side by side relationship of the dual implants whenimplanted.

[0237] As shown in FIGS. 7C and 7D, a Dual Outer Sleeve 340 consistingof a pair of hollow tubes is then introduced over the side by side LongDistractors protruding anteriorly from the spine. The Dual Outer Sleeve340 is comprised of two hollow tubular members identical in sizedisplaced from each other ideally the sum of the difference between theminor and major diameters of both implants combined, but not less thanthat difference for one implant, as it is possible to have the threadsof one implant nest interposed to the threads of the other, such thatthey both occupy a common area between them. However, while thepreferred embodiment is slightly greater than two times the differencebetween the major and minor diameters of the implant (the sum of both)the distance may be considerably greater. Whereas in the preferredembodiment extending tubular portions 348 of instrument 340 areparallel, when the area between them 350, is sufficiently great, theseelements may be inclined or declined relative to each other such thatthey either converge or diverge at their proximal ends. Paired tubularstructures 348, may be bridged in part or wholly throughout theirlength, but are rigidly fixed by Foot Plate 344. In its preferredembodiment, a top view shows the Foot Plate to be essentiallyrectangular, but without sharp corners.

[0238] Other shapes can be utilized. In side view 7D it can beappreciated, that Foot Plate 344 is contoured so as to approximate theshape of the vertebrae anteriorly. Extending forward from Foot Plate 344are multiple sharp prongs 342 sufficiently long to affix them to thevertebrae. The prongs 342 are limited in length so as to not penetratetoo far posteriorly and number from 2 to 10, but preferably 6. As theDual Outer Sleeve 340 is driven forward utilizing Dual Driver Cap 420,of FIG. 7E, engaging the rearward end 352, the prongs 342 extending fromFoot Plate 344 are embedded into the opposed vertebral bodies untiltheir forward motion is inhibited by the curved Foot Plate 344 becomingcongruent to and being stopped by, the anterior aspect of the vertebralbodies.

[0239] As already taught in FIG. 5, the Dual Driver Cap 420 is of thesame design as Single Driver Cap 160, in that there is a recess 354 asper 168, allowing the Outer Sleeve to be fully seated without impedingthe rearward projection of the Long Distractor unit. However, unlike inCap 160, area 354 is more relieved as it is unnecessary for the Dual Cap420 to contact the Long Distractor through portion 110 to inhibit itsforward motion, as the Foot Plate 344 functions to that effect. Further,the Dual Cap 420 for the Dual Outer Sleeve 340 is correspondingly dualitself and engages the rearward facing dual tubular portion 352. Oncethe Dual Outer Sleeve has been fully seated, the vertebrae adjacent theinterspace to be fused are rigidly held via Foot Plate 344 and theprongs 342. Thus, it is possible to remove either one, or if desired,both of the Long Distractor rods utilizing Long Distractor puller 200,as per the method already described. It is then the surgeon's choice towork on one or both sides of the spine. As per previous discussion, thesurgeon may drill the interspace utilizing the Inner Sleeve 242 or leavethe Long Distractors in place as per the “Trephine Method”.

[0240] Tapping, if necessary, and the insertion of the implants thenoccurs through the protective Outer Sleeve 340. Once the implants havebeen fully inserted, the Outer Sleeve is removed.

[0241] Having utilized the Drill method, or “Trephine Method”, with orwithout an Inner Sleeve to prepare the fusion site, it is the preferredembodiment to leave the Outer Sleeve 340 in place as it provides for theideal placement and alignment of the Tap 280 and implant I.

[0242] It is anticipated that the surgeon wishing to work deep withinthe interspace, or preferring the ability to directly visualize the tapbeing used, or the implant being inserted, may choose to remove theOuter Sleeve after the insertion of the first prosthesis to maintainstability, or prior to that, which while not the preferred embodiments,are nevertheless within the scope of the present invention.

[0243] Alternative Methods to the Preferred Embodiment for Method ofAnterior Interbody Fusion

[0244] As previously described for the posterior lumbar spine,alternatively, one can employ the “Trephine Method” as has beendescribed in detail.

[0245] As a further alternative, it should be noted that the key elementin the anterior method is the use of the predistraction principle, wheresuch distraction is maintained by the Outer Sleeve with or without theLong Distractor. Therefore, once the preparation of the interspace hasbeen completed, while not the preferred embodiment, it is neverthelesswithin the scope of this invention that one could remove the OuterSleeve as there are no neural structures requiring protection, andinsert the implants directly rather than through the Outer Sleeve.

[0246] As yet a further alternative of this method, where the height ofthe distracted interspace is such that the diameter of the implantrequired to span that height and to embed with sufficient depth into theopposed vertebral bodies is such that it is not possible to place twosuch implants side by side, then only a single implant which may be ofsignificantly increased diameter, is used and placed centrally withinthe interspace rather than to either side. The placement of a singularcentral graft via the present invention method and instrumentation is inkeeping with the methods already described and can be performed usingeither a drill or the “Trephine Method”.

[0247] Referring to FIGS. 16-18, a cylindrical embodiment of the spinalimplant I of the present invention is shown. In FIG. 16 the implant I isshown attached to the insertion device 350. In FIGS. 17 and 18 theimplant I is shown installed in the disc space D, between the adjacentvertebrae.

[0248] The cylindrical implant I comprises a hollow tubular member whichin the preferred embodiment is made of an ASTM surgically implantablematerial, preferably Titanium. The cylindrical implant I is closed atone end and open at the other end covered by a cap 394. The cylindricalimplant I has a series of macro-sized openings 390 through the sidewalls of the cylindrical implant I. A series of external threads 392 areformed on the circumference of the cylindrical implant I. Any variety ofthreads may be used on the implant. The cap 374 has a hexagonal isopening 394 for tightening the cap 374.

[0249] While the present invention has been described in associationwith the implant of a threaded spinal implant, it is recognized thatother forms of implants may be used with the present method. Forexample, dowels, made from bone or artificial materials, knurled orirregularly shaped cylinders or spheres, or any other shaped implantsthat can be introduced through the outer sleeve may be used. Being ableto perform the procedure through the outer sleeve permits the procedureto be performed safely and quickly, and more accurately.

I claim:
 1. A distractor, comprising: a distraction head having alongitudinal axis and a first pair of opposed surfaces extendingsubstantially along said longitudinal axis and defining a first workingdistraction height approximating a normal disc space height and a secondpair of opposed surfaces extending substantially along said longitudinalaxis and defining a second working distraction height approximating asecond normal disc space height, said distraction head rotatable betweensaid first distraction height and said second distraction height byrotating the distraction head about said longitudinal axis.
 2. Thedistractor of claim 1, wherein said first pair of opposing surfaces areplanar surfaces extending in a parallel alignment along saidlongitudinal axis.
 3. The distractor of claim 2, wherein said distractorhead includes: a distractor tip having a rounded leading edge to permitinsertion of said distractor head to directly achieve said secondworking distraction height; and a pair of inclined surfaces extendingfrom said leading edge to said first pair of opposing surfaces.
 4. Thedistractor of claim 1, wherein said distractor head includes roundedsurfaces adapted to engage and urge bone apart to said seconddistraction height during rotation.
 5. The distractor of claim 1,further comprising a shaft joined with said distractor head.
 6. Thedistractor of claim 5, wherein said shaft is integrally joined to saiddistractor head.
 7. A spinal distractor for use in spinal surgery fortemporarily positioning two adjacent vertebral bodies in selectedrelationship to restore the height of the disc space therebetween priorto inserting an implant into the distracted disc space, said spinaldistractor comprising: a body having a proximal end, a distal endopposite said proximal end, and a mid-longitudinal axis therebetween;and an extension extending from said distal end of said body andconfigured to contact the adjacent vertebral bodies upon insertion intothe disc space between the two adjacent vertebral bodies, said extensionbeing removably attached to said body, said extension being adapted tobear against adjacent endplates of the two adjacent vertebral bodies,said extension having a first portion for bearing against one of theadjacent endplates and a second portion for bearing against the other ofthe adjacent endplates to maintain the adjacent vertebral bodies inselected relationship, said extension having a height no greater thanthe surgically corrected height of the disc space, said distal end ofsaid body being configured to prevent said body from entering the discspace between the endplates of the adjacent vertebral bodies when saidextension is inserted into the disc space.
 8. The spinal distractor ofclaim 7, wherein said body has a shoulder at the juncture of saidextension and said body for preventing said body from entering the discspace between the endplates of the adjacent vertebral bodies.
 9. Thespinal distractor of claim 7, wherein said distal end of said body has acircular cross-section.
 10. The spinal distractor of claim 7, whereinsaid extension includes a head proximate the juncture of said extensionand said body, said head being dimensioned to prevent entry into thedisc space.
 11. The spinal distractor of claims 10, wherein said headhas a low profile so as to minimize protrusion of said head from the twoadjacent vertebral bodies.
 12. The spinal distractor of claim 7, whereinsaid extension has a tapered front end to facilitate insertion of saidextension into the disc space.
 13. The spinal distractor of claim 7,wherein said extension has surface irregularities.
 14. The spinaldistractor of claim 13, wherein said surface irregularities includeratchetings.
 15. The spinal distractor of claim 13, wherein said surfaceirregularities include knurling.
 16. The spinal distractor of claim 7,wherein said body is configured to engage an extraction device forextracting said extension from the disc space.
 17. The spinal distractorof claim 16, wherein said body includes a mating member for mating withthe extraction device.
 18. The spinal distractor of claim 7, furthercomprising an impacting surface proximate the juncture of said body andsaid extension for flattening portions of the exterior surface of thetwo adjacent vertebral bodies.
 19. The spinal distractor of claim 7, incombination with a guard member having an opening for providingprotected access to the disc space and the adjacent vertebral bodies,said spinal distractor adapted to pass through said opening of saidguard.
 20. The combination of claim 19, wherein said proximal end ofsaid body of said distractor is configured to allow said guard to beplaced over said proximal end of said body.
 21. The combination of claim19, in combination with a bone removal device having a portion sized formovement through said opening for forming through said guard animplantation space at least in part across the surgically correctedheight of the disc space.
 22. The combination of claim 21, wherein saidbone removal device is one of a drill, a trephine, and a reamer.
 23. Thecombination of claim 7, further in combination with a spinal insert. 24.The combination of claim 23, wherein said spinal insert is one of adowel, an interbody spinal implant, and an interbody spinal fusionimplant.
 25. The combination of claim 23, wherein said spinal insertcomprises at least in part bone.
 26. The combination of claim 23,wherein said spinal insert is a bone graft.
 27. The combination of claim23, further in combination with a fusion promoting substance.
 28. Thecombination of claim 27, wherein said fusion promoting substance isbone.
 29. The combination of claim 23, further in combination with apress for compressing said fusion promoting substance into said spinalinsert.
 30. The combination of claim 23, further in combination with animplant driver configured to insert said spinal insert into theimplantation space formed by said bone removal device.
 31. Thecombination of claim 19, in combination with a tap for insertion throughsaid guard for tapping the two adjacent vertebral bodies.